Toilet that generates energy from human waste

Five years after the Bill and Melinda Gates Foundation first challenged the world to design a sustainable and inexpensive toilet, researchers from Cranfield University may have a viable contender. It’s known as the Nano Membrane Toilet, and it was funded by the Gates Foundation in September 2012 for US $710,000.

March 22 is World Water Day, an appropriate time to highlight the grim fact that more than 2.4 billion people around the world still live in unsanitary conditions. Without access to clean running water, these at-risk communities face life-threatening sanitation-related diseases.

The Nano Membrane toilet’s design is meant to offset this scarcity. It’s waterless, easy to use, and provided it receives additional funding for field tests, could very well be part of the future of sanitation.

Alison Parker, a lecturer in International Water and Sanitation at Cranfield Water Science Institute, says her team’s new design is meant to serve poor urban areas, as those will be easiest to accommodate.

“It will be very hard to carry out the scheduled maintenance” in remote areas, Parker tells Tech Insider, mostly because the toilet needs maintenance every six months at a minimum to replace certain parts. “Instead, the toilet will be used in dense urban areas where a number of factors make providing good sanitation very challenging, but where it would be possible to facilitate visits from a maintenance technician.”

The toilet’s actual design is rather complex.

After a person has done their business and closed the lid, the rotating toilet bowl turns 270 degrees to deposit the waste in a vat underneath. A scraper tool then wipes off any residual waste from the bowl.

The solid waste stays on the bottom while the liquid rises to the top.

Extremely thin fibres, known as nanofibres, are arranged in bundles inside the chamber. They help move the water vapour that exists as part of the liquid waste into a vertical tube in the rear of the toilet.

Next, water passes through specially designed beads that help condense the vapour into actual water, which flows down through the tube and settles in a tank at the front of the toilet.

As for the solid waste that’s left behind, a battery-powered mechanism lifts the remaining matter out of the toilet and into a separate holding chamber. There it’s coated in a scent-suppressing wax and left to dry out.

Every week, a local technician visits the community to remove the solid waste and water, and replace the toilet’s batteries if needed. Residents can then use the water for tending to their plants, cleaning their homes, cooking, and bathing. The solid waste ends up at a thermo-processing plant to be turned into energy for the community.

According to Parker, one toilet can accommodate up to 10 people for no more than $0.05 per day, per user – in line with the Bill and Melinda Gates Foundation’s original criteria for the prize. Field testing will begin later this year, Parker says.